Illuminated instrument face



Patented Aug. 7, 1951 ILLUMINATED INSTRUMENT FACE James D. Lash,Cleveland Heights, Ohio, assignor to General Electric Company, acorporation of New York Application June 2,1950, Serial No. 165,683 1Claim. (Cl. 116-129) My invention relates to clocks, meters, or othersimilar instruments, and illuminated faces or dials for suchinstruments. More particularly, my invention is directed toward theself-illumination of faces for clocks or similar instruments, that is,in which the illumination comes from within the body of the instrumentitself and outside illumination sources are not necessary.

One object of my invention is to promote uniformity of self-illuminationover the entire face of the clock dial or other instrument face. Anotherobject of my invention is to provide high visibility and readability ofthe instrument face when outside light, such as daylight, strikes theindicating face of the instrument, and to provide high visibility of theinstrument face if the self-illumination source should fail. A furtherobject of my invention is to provide a self-illuminated instrument facewhich is inexpensive, simple to make, attractive, and effective for thepurpose required. Still another object of my invention is to provide aconcealed light source for a selfilluminated instrument, the addition ofthe light source requiring little or no added space in standard clocks,meters or other similar instruments.

The objects of my invention are met generally by applying the edgelighting principle to the faces of clocks, meters, or similarinstruments, and by inserting the light source within the transparentplate which forms the instrument face. Other arrangements laterdescribed in crease the visibility and readability of the instrumentface when it is in use.

Other objects and further details of that which I believe to be noveland my invention will be clear from the following description and claimtaken with the accompanying drawing in which is illustrated an exampleof instrument embody-` ing the present invention and incorporating myimproved form of edge lighting and other features.

In the drawing, Fig. 1 is a front elevation of a clock according to myinvention; Fig. 2 is a side section of the clock of Fig. l; and Fig. 3is a front elevation of a background contrast sheet or disk used in theclock of Figs. 1 and 2.

Although I have shown a clock in the drawing, with the usual face,bearing numbers and having hands, it is obvious that the invention maybe applied to any instrument having a dial or similar face, and having ahand or pointer which co-operates with indicia on the dial. The clockhas a usual opaque outer body or enclosing case l in the front of whichis an opening 2 through which the face is visible. Of course,

2 this face opening may be covered by glass in the usual fashion ifdesired. l

Inside of the instrument case is mounted a motor or other mechanism 3which drives the pointer of the instrument, in this case 'the hands 4and 5 of the clock. A suitable and usual driving shaft 6 extends betweenthe motor and the hands.

The casing of the clock serves as a housing for the illuminating partsfor the clock face and shields or conceals the source of light fromdirect view. The face of the clock is in the form of a dial or faceplate I located directly in back of the opening 2 of the clock case andhaving lower portions extending below the face opening and thereforeshielded from view by the opaque material of the clock case. The dialplate is made of a transparent material such as the plastic known asPlexiglas or it may be clear glass, or the clear plastic sold as Luciteor other transparent material with optical characteristics similar tothose of the materials mentioned. Within the border of the face platebut outside of the area exposed by the opening 2, I provide a hole 8,for purposes which will later be evident.

The outer edges of the face plate or dial l and the entire inside edgesof the hole are smoothed and polished. The outside edge of the faceplate is then given a mirror finish as by gluing tin foil around thispolished outside edge. Obviously, aluminum paint, silvering or othertypes of mirror finish could be used instead of the tin foil. Thepurpose of this mirror edge is to reflect light back and forth inside ofthe face plate, to ob- Vtain good utilization of light and uniformillumination of the figures, etc. on the clock dial.

Placed inside of the hole 8 is the source of il` lumnation, shown hereas an incandescent or glow type electric lamp bulb 9. As shown, thisbulb may be suitably supported within the clock case as by a bracket l0extending from the housing of the motor 3 and supplied with a suitablesource of electrical power in any desirable fashion. When lit, this lampbulb illuminates the interior of the transparent face plate, the mirroredge on the plate spreading the illumination in a uniform manner.

The indicia on the instrument, in this case the numbers from one totwelve on the dial of the clock, should be easily readable from theillumination supplied by the light source alone. For this reason, Iprefer to paint these numbers in white or light-coloredl opaque paint,preferably of a flat or dull nature. A glossy paint might be used. butthe effects are not as good as when a dull paint is used. These numbersare painted on the back surface of the face plate as shown at Il forbest effect, it having been found that this arrangement gives the bestbrightness effect. The numbers might be painted in translucent paint onthe front face of the plate, but this arrangement would result in lowerbrightness of the indicia with the rest of the arrangement disclosed.

The central space within the. dial is provided with a light dispersingandbackground producing area I2 shown here as a screen composed of anumber of White dots. numbers, are preferably made of opaque white orlight-colored paint on the back surface of the face plate, thediscontinuous painted area represented by the dots being kept at aminimum for maintaining reasonably uniform lighting of the numbers onthe dial while at the same time providing a background for showing thehands of the clock in silhouette. In place of the spaced dots, spacedconcentric circles, or a striped or checkered pattern could be used aslong as the required level of illumination is maintained.

In place of the light or white-colored paint mentioned above for thenumbers and for the central area on the clock dial, it is obvious thatsilk screening, engraving or color tints could be used.

For better daytime and nighttime visibility, a background sheet or plateI3 is located and supported (as by cementing in the case) in slightlyspaced relation from the back of the dial plate within the clock case.This background sheet or disk has a white or light-colored centerportion I4 located behind the white dotted area of the dial plate and acircumferential black or darkcolored area I5 behind the number carryingsection of the face plate. Thebackground sheet may be made of metal,cardboard, or other suitable stii material, and the areas I4 and I5 maybe made by painting the front surface of the background sheetor bygluing colored sections of paper thereon. This provides an opaquebackground for the entire face of the clock, which is close to but notin optical contact with the back surface of the dial or face plate. Ofcourse, the drive shaft 6 for the hands extends freely through suitableholes I 6 and I1 in the background sheet andthe dial plate.

'Ihe clock hands 4 and 5 are made of the usual materials such as metal,opaque, and preferably` of dark color for contrast with the screened ordotted area on theface plate and the white or light-colored area on thebackground plate. As shown, the hands of the clock are located in frontof the front surface of the face plate.

By using the discontinuous dotted or screened central section instead ofa solid area of paint or other reflecting material on the face plate, auniform illumination over the entire face is obtained without detractingfrom proper brightness of the numbers, and a light background isprovided against which the clock hands are seen easily in silhouette.The white or light background area I4 of the background plate, togetherwith the white or light-colored, dotted or screened area on the dialplate, gives good daytime as will as nighttime legibility to the face ofthe clock or other instrument. This is important where, as is often thecase, outside illumination is at a level higher than the illuminationThese dots, like the 4 level of the clock face itself. This is alsoimportant in case the internal illumination source fails, andillumination from outside has to be depended upon.

The use of a specular reflecting surface around the edge of the face ordial plate. and the placing of the lamp in the hole through the plateoutside of the dial-reading area give maximum utilization of the lightand require the minimum of space for the light source. The dark areaaround the circumference of the background plate in back of the numbersfurnishes a contrasting field against which the light-colored numbersare easily seen both day and night.

If the clock numbers are made of a dark color, they should be placed onthe front face of the dial and made opaque, and the screened or dottedarea should be extended in back of the numbers with the entirebackground plate made in white or light color for best results. However,it is not believed that this arrangement is as effective as thearrangement shown, using the light-colored numbers and the dark-coloredbackground therefor.

As will be evident from the foregoing description, certain aspects of myinvention are not limited to the particular details of construction ofthe example illustrated, and I contemplate that various and othermodifications and applications of the invention will occur to thoseskilled in the art. It is therefore my intention that the appended claimshall cover such modifications and applications as do not depart fromthe true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

A self-illuminated clock dial comprising a transparent face plate with afront surface, a back surface and outer reflecting edges, an opaqueshield covering the edges of sa'id plate and a portion of the plate fromview at the front, indicia of light color painted on the back surface ofthe plate in an area not covered by said shield, said plate having ahole therein in said shield-covered portion of said plate, a lightsource located in said hole for illuminating said indicia from theinterior of said plate, an opaque pointer of dark color mounted to moveover the front surface of the plate opposite said indicia, an opaquelight-colored discontinuous screen area comprising spaced opaque dotspainted on the back surface of said plate adjacent saidindiciurdertherpathwflmovementrpfnsaid pointer. and a ybackground sheetclose to but optically spaced from said back surface of said face plateand providing a dark-colored background behind said indicia-carryingarea of said face plate and a light-colored background behind saidscreen area for contrasting with said dark pointer.

JAMES D. LASH.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,994,950 Hoffritz Mar. 19, 19352,278,520 Klein Apr. 7, 1942 2,365,864 Chapman Dec. 26, 1944 2,083,924Scantlebury June 15, 1937

